Combined grinding and leaching apparatus for ores and wastes and methods of use thereof

ABSTRACT

Disclosed is an apparatus that is an attrition mill for grinding or comminuting ores, mine wastes, and radioactive wastes some of which may comprise metals, which may include uranium and/or cesium and/or mercury and/or thorium and/or rare earth elements. Also disclosed are processes that employ the apparatus for combined grinding and optionally leaching metals from ores and wastes. Some such methods comprise an optional step of grinding and mixing the ore or waste with a solid inorganic base with water addition or with an aqueous inorganic base, follow by a step of grinding and mixing the ore or waste with an aqueous inorganic acid with or without leaching salt addition, to solubilize the metals present in the ore or the waste. The disclosed apparatus and methods, in some embodiments, enable efficient grinding and attrition of ores substrates and mine wastes even without need for grinding media.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the prior right of Great Britain patentapplication 1709612.4 filed Jun. 16, 2017, which is incorporated hereinby reference.

TECHNICAL FIELD

The present specification generally relates to ores and wastesprocessing and more particularly to apparatuses and methods for grindingof the ores and wastes, and optionally leaching metals from the ores andwastes. More specifically, the present disclosure relates to anapparatus for the grinding or comminution of ores, mine wastes andradioactive wastes, and corresponding methods.

BACKGROUND

Important needs for the mining industry in relation to actinide elements(U and Th) are the management of radioactive mine wastes and theseparation of actinide elements during rare earth elements (REE)production. In Canada, the wastes inventory at the end of 2010 reached214 million tons of uranium tailings and 174 million tons of U miningwaste rock (LLRWMO, 2012). Radioactive elements of uranium and thoriumare usually associated with rare earth deposits. Conversely, uraniumores often contain significant concentration of rare earth elements. Theseparation of U and Th from rare earths is often a big concern in therare earth industry in order to manage use and extraction of radioactivenuclides (Zhu et al., 2015). Due to recent increases in both uranium andrare earth element prices, there is renewed interest in uranium and rareearth mine sites for developing new ore bodies as well as re-processingthe historic waste rock piles and tailings impoundments. Therefore,extracting the uranium would be advantageous for decreasing thelong-term radioactivity of wastes and, consequently, the cost of thelong-term disposal process. Consequently, there are safety and economicincentives for the extraction of metals before subjecting radioactivecemented wastes to a stabilization process.

The technology for recovering uranium from its most common ores is wellestablished and a vast amount of information is available in thetechnical literature (e.g. Merritt, 1971; Wilkinson, 1962). Uranium isnormally leached from its ores with sulfuric acid, separated fromimpurities using solvent extraction or ion exchange, and precipitatedwith magnesium or ammonium hydroxide to yield a commercial product,known as “yellow cake”. Extraction of rare earth elements is also wellestablished. The extractive metallurgy of rare earth elements frommonazite sand, bastnasite ore, and phosphate rock of igneous origin wasdescribed by Habashi (2013). This includes mineral beneficiation,leaching methods, fractional crystallization, ion exchange, solventextraction, precipitation from solution, and reduction to metals. Bycontrast, cemented radioactive wastes differ significantly from commonores and have a unique mineralogy, a high alkaline nature, a relativelylow U grade, and a high content of Ca (^(˜)35%), SiO₂ (^(˜)20%) and Hg(^(˜)1,500 ppm). The composition of the radioactive wastes posessignificant impediments to the extraction and recovery of metals usingconventional technologies. The high Ca content will interfere with bothcarbonate leaching and sulfuric acid leaching by forming large amountsof CaCO₃ and CaSO₄, respectively. Furthermore, the high silica contentof the cemented radioactive wastes may lead to the formation ofcolloidal silica, which is known to create severe problems inhydrometallurgical circuits (Queneau and Berthold, 1986).

A process, using sulphuric acid and potassium iodide, was developed foractinides and lanthanides recovery from nuclear wastes, mine wastes andrare earth elements ores (Reynier et al., 2015; Reynier et al., 2016).The optimization of the grinding and leaching processes is an importantstep towards the green processing of ores and wastes. There is a need toincrease leaching and grinding efficiencies, reduce process steps andenergy consumption, simplify equipment, and reduce both the capitalexpenditure and the operational expenditure (CAPEX/OPEX). It issubmitted that combining grinding and leaching in a single apparatuswould present these advantages.

A known apparatus for improved grinding is the attrition mill which wasinitially developed by Dr. Andrew Szegvari in 1945 and large productionunits are now available for wet, dry and even cryogenic grinding. Inthis apparatus, grinding is achieved by a random agitation of a grindingmedia (steel balls) in a stationary tank (grinding chamber) by means ofrotating shaft and arms. Grinding occurs mainly through shearing amongthe particles themselves and/or in interaction with the grinding media.Finer material is usually obtained by attrition in comparison to othermechanical grinding mechanisms such as impact and compression.

The attrition mill technology may be selected for optimization of thegrinding and leaching processes in radioactive waste fragmentation.Known attempts, using grinding media, have been made for example in U.S.Pat. No. 5,007,589, CA 2,022,300, U.S. Pat. No. 4,242,129, U.S. Pat. No.6,835,230, WO 2004/005556, U.S. Pat. No. 2,137,051 and US 2013/0099033.There is a wide variety of disadvantages and challenges related to theknown techniques for grinding ores or wastes, and metals leaching fromores and wastes. There is indeed a need for a technology that overcomesat least some of the disadvantages of the known methods in the field.

In radioactive waste processing, grinding media can hardly be separatedfrom the pulp after grinding and can neither be disposed with theresidual waste as it would increases significantly the weight and/orvolume of the waste and the cost for long term storage. Moreover, thepossibility of using a removable and less sturdy grinding chamber, whichcould serve for unmolding the waste form its container before grindingand subsequently for lixiviation and as a disposal vessel would be abeneficial advantage. Such a combined process would avoid pulp transferamong processes and the related risk of contamination, which must beminimized in any radioactive waste processes.

In rare earth processing, grinding in the absence of grinding media mayalso provide some advantages if satisfactory lixiviation efficiency canbe achieved at a larger grain size. A ratio of grinding media to the oreis usually more than 15 to 1, and a lot of grinding energy is thereforeused for agitating the media itself within the grinding chamber. Theenergy embodied in the wearing and replacement of the grinding mediaadds another 33% to the grinding energy. Grinding in the absence ofgrinding media requires less energy and entrains important cost savingsand reduction of GHG emissions in the mining industry considering thatgrinding energy represents 90% of the energy used in rock fragmentation,40% of the energy used in open-pit and 3% of world electrical energy.The impact on mine production and footprint reduction is also importantconsidering in addition the space occupied by the grinding media in thegrinding chamber. Frequency of liner replacement, which causes 50% ofthe mill downtime, may also be reduced significantly in the absence ofgrinding media.

Grinding at a coarser grind may provide some important environmentalbenefits considering that water retention is less in a coarse graintailing pond, and the eventual damage caused to the neighborhood by atailings pond leakage would be then be reduced significantly. However,there is a general expectation in the art that grinding media arerequired in many circumstances to achieve a desired degree of grindingor communition of ores, mine wastes etc.

In view of the above, there is a need for improvements in apparatusesfor grinding or comminuting of ores, wastes and earth substrates, andcorresponding methods.

SUMMARY

The present specification responds to the above need by providing anapparatus for grinding or comminuting of ores, substrates and wastessuch as mining wastes and radioactive wastes. Also disclosed arecorresponding methods for grinding and comminuting ores, mine wastes,and radioactive wastes including those comprising metals such as uraniumand/or cesium and/or mercury and/or thorium and/or rare earth elements,and optionally for dissolution of these from ores and wastes.Advantageously, though not necessarily, such apparatuses and methods maypermit grinding and comminution without the need, or with reduced need,for grinding media.

Exemplary embodiment (1) provides an apparatus for grinding orcomminuting a metal-containing ore, substrate, mine waste, orradioactive waste, the apparatus comprising:

-   -   a. a container comprising inner walls that define an open end        and a closed end for the container, and a lumen for retaining        the ore, with two or more elongate ribs projecting inwardly from        the walls and extending from the closed end towards the open end        of the container;    -   b. a powered, rotatable spindle extending into and axially        aligned with the container, substantially equidistant from side        walls of the inner walls of the container;    -   c. a plurality of grinding arms arranged about and extending        from the spindle such that each comprises at least one free end        that passes with a clearance of from 0.01 mm to 20 mm from each        of the ribs on the inner walls of the container, as the spindle        is rotated; and    -   d. a motor to drive axial rotation of the spindle and attached        grinding arms within the container,    -   wherein the apparatus grinds or comminutes the metal-containing        ore, substrate or mine waste by grinding and attrition        optionally absent grinding media.

Exemplary embodiment 2 provides the apparatus of exemplary embodiment 1,wherein each grinding arm extends through and extends upon each side ofthe spindle such that each grinding arm comprises two free ends thateach pass with a clearance of from 0.01 mm to 20 mm from each of theribs on the side walls of the container, as the spindle is rotated.

Exemplary embodiment 3 provides the apparatus of exemplary embodiment 1,wherein successive grinding arms are arranged helically about thespindle such that each successive grinding arm extends at an acute anglefrom the axis of the spindle relative to its adjacent grinding arm onthe spindle, and all grinding arms extend about 90 degrees from an axisof the spindle.

Exemplary embodiment 4 provides the apparatus of exemplary embodiment 1,wherein each grinding arm extends about 90 degrees from each adjacentgrinding arm along the spindle, and all grinding arms extend about 90degrees from an axis of the spindle.

Exemplary embodiment 5 provides the apparatus of exemplary embodiment 1,wherein the grinding arms are at least substantially uniformlyelliptical in cross-section, or at least substantially uniformlycircular in cross-section, and optionally the grinding arm or armsadjacent the closed end of the container have a substantially square orrectangular cross-section.

Exemplary embodiment 6 provides the apparatus of exemplary embodiment 1,wherein the spindle and attached grinding arms are movable axiallyrelative to the container such that the spindle and grinding arms can beremoved from the container, optionally by a telescoping attachment arm.

Exemplary embodiment 7 provides the apparatus of exemplary embodiment 1,wherein the container comprises three or more ribs, at least a portionof which are arranged at least substantially parallel to one another ina radially symmetric manner about the inner walls of the container.

Exemplary embodiment 8 provides the apparatus of exemplary embodiment 7,wherein the container defines a cylindrical lumen and the side innerwalls comprise six ribs arranged parallel to one another, at least aportion of which extend a length of the side inner walls from the closedend to the open end of the container, in a radially symmetricalarrangement 60 degrees apart about the axis of the container.

Exemplary embodiment 9 provides the apparatus of exemplary embodiment 1,wherein the inner walls of the container define a cylindrical lumen forthe container, defined by a continuous, cylindrical side wall portionextending between the open and closed ends of the container, and asubstantially circular floor portion at the closed end of the container,the elongate ribs extending such that they radiate from a centre of saidcircular portion and continue with a substantially parallel arrangementalong said cylindrical side wall portion from the closed end to the openend of the container.

Exemplary embodiment 10 provides the apparatus of exemplary embodiment1, wherein the plurality of grinding arms comprises from 2 to 20grinding arms.

Exemplary embodiment 11 provides the apparatus of exemplary embodiment1, wherein clearance between the free ends of the grinding arms and theribs is from 0.1-5 mm.

Exemplary embodiment 12 provides the apparatus of exemplary embodiment9, wherein the grinding arms comprising one or more grinding arms thatextend from a free-end of the spindle, which during operation androtation of the spindle pass adjacent the portion of the elongate ribsthat radiate from a centre of the substantially circular floor portionat the closed end of the container, with a clearance of from 0.5-10 mm,preferably less than 5 mm, preferably less than 3 mm.

Exemplary embodiment 13 provides the apparatus of exemplary embodiment1, wherein the powered, rotatable spindle and/or the grinding armscomprise one or more magnets for collecting magnetic metal components ofthe ore, substrate or mine waste.

Exemplary embodiment 14 provides the apparatus of exemplary embodiment1, further comprising air flotation means to add pressured air into theore, substrate or mine waste being processed, the air flotation meanscomprising air channels extending within at least some of the grindingarms, each of which exits at least part way along its respectivegrinding arm, and an air pump to force air through the air channels andout of the grinding arms during rotation of the spindle.

Exemplary embodiment 15 provides for a use of the grinding orcomminuting apparatus of any one of exemplary embodiments 1 to 14, forgrinding or comminuting a metal-containing ore, substrate or mine waste.

Exemplary embodiment 16 provides for a method for grinding orcomminuting a metal-containing ore, substrate, mine-waste, orradioactive waste, comprising the steps of:

-   -   a. adding the metal-containing ore, substrate or mine waste to        the container of the apparatus of any one of exemplary        embodiments 1 to 14;    -   b. optionally adding a grinding media to the container;    -   c. applying power to the motor thereby to rotate the spindle and        attached grinding arms;        wherein steps a. and b. if present may be performed in any        order.

Exemplary embodiment 17 provides the method of exemplary embodiment 16,further comprising a step of adding to the metal-containing ore,substrate or mine waste, either before, together with or after step a.,an aqueous inorganic acid at a concentration of between about 1M andabout 9M, at a temperature of less than about 100° C., to solubilize atleast a portion of the at least one metal, thereby to produce a mixtureof a metal-rich leachate and a metal-poor ore or waste.

Exemplary embodiment 18 provides the method of exemplary embodiment 16or 17, wherein the metal comprises uranium, cesium, mercury, thorium,rare earth elements, or combinations thereof.

Exemplary embodiment 19 provides the method of exemplary embodiment 16or 17, wherein the waste is a cemented radioactive waste or aradioactive mine waste.

Exemplary embodiment 20 provides the method of exemplary embodiment 17,wherein the inorganic acid comprises sulfuric acid, nitric acid,hydrochloric acid, phosphoric acid, mixtures thereof, or combinations ofinorganic acid and salts thereof.

Exemplary embodiment 21 provides the method of exemplary embodiment 17,further comprising, either before or after the adding of the aqueousinorganic acid, a step of adding an aqueous inorganic base with theaddition of water, or with an aqueous organic base at a concentration offrom about 1M to about 7.5M, to solubilize at least a portion of the atleast one metal providing an aqueous mixture. Exemplary embodiment 22provides the method of exemplary embodiment 17 or 21, further comprisinga step of: separating the mixture of a metal-rich leachate and ametal-poor ore or waste.

Exemplary embodiment 23 provides the method of exemplary embodiment 15or 16, further comprising addition of a leaching salt, wherein theleaching salt comprises a halogen salt such as potassium iodide or amercury salt such as mercury nitrate, or any combination thereof.

Exemplary embodiment 24 provides the method of any one of exemplaryembodiments 16 to 23, wherein the method is performed absent anygrinding media.

Certain other exemplary embodiments provide a process for combinedgrinding and leaching of at least one metal from ore or waste comprisingthe at least one metal, the process comprising:

a) a combined attrition and leaching step comprising grinding and mixingthe ore or waste with an aqueous inorganic acid at a concentrationbetween about 1 M and about 9 M, at a temperature lower than about 100°C., to solubilize at least a portion of the at least one metal, therebyproducing a mixture of a metal-rich leachate and

a metal-poor ore or waste; and

-   -   b) a separation step comprising separating the metal-rich        leachate and the metal-poor ore or waste.

Other exemplary embodiments provide s process for combined grinding andleaching of at least one metal from ore and waste comprising the atleast one metal, the process comprising:

a) a basic combined attrition and leaching step comprising grinding andmixing the ore or the waste with a solid inorganic base with theaddition of water, or with an aqueous inorganic base at a concentrationbetween about 1 M and about 7.5 M, to solubilize at least a portion ofthe at least one metal providing an aqueous mixture;

b) an acidic combined attrition and leaching step comprising grindingand mixing the ore or waste with an aqueous inorganic acid at aconcentration between about 1 M and about 9 M, at a temperature lowerthan about 100° C., to solubilize at least a portion of the at least onemetal thereby producing a mixture of a metal-rich leachate and ametal-poor ore or waste; and

c) a separation step comprising separating the metal-rich leachate andthe metal-poor ore or waste.

Additional embodiments, aspects and features of the invention will bedescribed and defined herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart to illustrate a process according to oneembodiment.

FIG. 2 is a flow chart of a process according to another embodiment.

FIG. 3 illustrates a side view of a container portion of an exampleapparatus.

FIG. 4 illustrates a top view of a container portion of an exampleapparatus.

FIG. 5 illustrates a side view of an attrition unit portion of anexample apparatus.

FIG. 6 illustrates a side view of an attrition unit portion of anexample apparatus comprising an axially magnetized metal cylinder.

FIG. 7 illustrates a side view of an attrition unit portion of anexample apparatus comprising magnetized metal bars.

FIG. 8 illustrates a side perspective view of an example apparatus withthe attrition mill mixer shaft arm removed axially from the containerportion.

FIG. 9 illustrates a top perspective view of the internal walls of thecontainer portion.

FIG. 10 illustrates a top perspective view of the container portion ofthe apparatus with the attrition mill mixer shaft arm inserted.

FIG. 11 illustrates a side perspective view of an example apparatus withthe attrition mill mixer shaft arm removed axially from the containerportion.

FIG. 12 illustrates a side perspective view of a close up of theattrition mill mixer shaft arm removed axially from the containerportion.

FIG. 13 illustrates a top perspective view of the inner walls of thecontainer portion with the attrition mill mixer shaft arm removed.

FIG. 14 illustrates a side perspective view of an example apparatus inoperation.

FIG. 15 illustrates a side perspective view of the apparatus with theattrition mill mixer shaft arm removed axially from the containerportion.

FIG. 16 illustrates a top perspective view of the inner walls of thecontainer portion with the attrition mill mixer shaft arm inserted.

FIG. 17 is a graph to show solubilization of U29 radioactive cementedwaste in an apparatus by combining grinding and leaching with sulfuricacid at different particle sizes and with or without rinsing (pulpdensity fixed at 20%, acid/cement ratio fixed at 1.75).

FIG. 18 is a graph to show solubilization of U29 radioactive cementedwaste in an apparatus by combining grinding and leaching with sulfuricacid at different pulp density and with or without salt (particle sizefixed at 12 mm, acid/cement ratio fixed at 1.75).

FIG. 19 is a graph to show solubilization of U28 radioactive cementedwaste in an apparatus by combining grinding and leaching with sulfuricacid at different salt concentrations (particle size fixed at 8 mm,acid/cement ratio fixed at 1.5).

FIG. 20 is a graph to show solubilization of Th, U, and REE from the 6ores in a modified attrition mill by combining grinding and leachingwith sulfuric acid with or without NaOH addition performed at roomtemperature during 1 h (pulp density fixed at 20%, acid concentrationfixed at 7.5 M).

FIG. 21 is graph to show solubilization of Th, U, and REE from 6 ores ina modified attrition mill by combining grinding and leaching with nitricacid with or without NaOH addition performed at room temperature for 1 h(pulp density fixed at 20%, acid concentration fixed at 7.5 M).

FIG. 22 is a graph to show solubilization of Th, U, and REE from the Core in a modified attrition mill by combining grinding and leaching withsulfuric acid with or without NaOH addition and salt addition (KI orHg(NO₃)₂) performed at 20° C. for 1 h (pulp density fixed at 20%, acidconcentration fixed at 7.5 M, salt concentration fixed at 0.06 M for KIand 0.03 M for Hg(NO₃)₂).

FIG. 23 is a graph to show solubilization of Th, U, and REE from the Core in a modified attrition mill by combining grinding and leaching withnitric acid with or without NaOH addition and salt addition (KI orHg(NO₃)₂) performed at 20° C. for 1 h (pulp density fixed at 20%, acidconcentration fixed at 7.5 M, salt concentration fixed at 0.06 M for KIand 0.03 M for Hg(NO₃)₂).

FIG. 24 is graph to show solubilization of Th, U, and REE from 3 ores ina modified attrition mill by combining grinding and leaching with nitricacid performed at 75° C. for 2 h at different pulp density and an acidconcentration fixed at 30%).

FIG. 25 is graph to show solubilization of Th, U, and REE from 3 ores ina modified attrition mill by combining grinding and leaching withdifferent acid (sulphuric, nitric, hydrochloric) performed at 75° C. for2 h with acid concentration fixed at 30%.

DEFINITIONS

“About”, when qualifying the value of a variable or property—such asconcentration, temperature, pH, particle size and so on—means that suchvariable or property can vary within a certain range depending on themargin of error of the method or apparatus used to evaluate suchvariable or property. For instance, the margin of error for temperaturemay range between ±1° C. to ±5° C.

“Attrition”, when pertaining to the solid waste (e.g. earth substrate,mine waste, rocks, optionally comprising water), means subjecting thewaste to agitation to induce physical wear of the waste and separationinto smaller waste particles. Attrition may also aid in desorbing finewaste particles from larger waste particles. The attrition may sometimeshelp enable diffusion of the metals from the waste fractions and/or finewaste particles into the aqueous solution. The attrition sometimes mayinclude techniques such as milling. An attrition step may be performedin conjunction with other actions, such as contacting the waste withwater, and the contacting step may include soaking, batch mixing,trickling, spraying, continuous flow-by, or various combinations of suchcontacting techniques.

“Contacting”, when pertaining to the ore or waste and an aqueousinorganic acid, means that those elements contact each other so as toenable diffusion of the metals from the waste phase into the acidsolution phase. The “contacting” will often be referred to as leachingherein and may include techniques such as soaking, batch mixing,trickling, spraying, continuous flow-by, or various combination of suchcontacting techniques.

“Inorganic acid” means an acid lacking a carbon atom and may be asulfuric acid nitric acid, hydrochloric acid, mixtures thereof, or acombination of acids and corresponding salts. It should also beunderstood that the inorganic acid may be a used or recycled acid.

“Inorganic base” means a hydroxide of alkali metals, or alkaline earthmetals or a molecule that has the ability to accept an electron.Inorganic base examples may include sodium hydroxide, potassiumhydroxide, calcium hydroxide, sodium carbonate, ammonia, or acombination thereof.

“Leaching Salt” means an ionic compound and may be a halogen salt, suchas iodine, chlorine, fluorine, bromine, or any combination thereof. Theleaching salt may be a mercury salt, such as mercury nitrate, mercurychloride, mercury iodide, mercury iodate, or any combination thereof.

“Metals” means the elements of interest which are included in the ores,mine wastes or radioactive wastes and for which there are safety andeconomic incentives for their extraction. Metals may for example includebut are not limited to uranium, thorium, cesium, mercury, rare earthelements, a combination thereof and/or other metal species.

“Metals-rich solution” means a solution containing the metals removedfrom the ore or waste during a leaching step. It should also beunderstood that for subsequent treatment of the solution to remove orrecover metals, the metals-rich solution from the initial step may becombined with solutions from other leaching or washing steps to form anoverall metals-rich solution. Thus, the metals-rich solutions may becombined with other streams, or be subjected to various other stepsbefore it is treated to recover one or more of the metals.

“Mine waste” means a waste, which was produced during mining operationsor related to mining activities. It should be understood that the minewaste might be radioactive or mixed with a non-radioactive waste atvarious points in the process in order to form an overall waste to meetcertain governmental or environmental standards.

“Radioactive waste” means a radioactive waste that may be in any state,liquid, solid, granular, or powder form and so on. It should beunderstood that the radioactive waste might be mixed with anon-radioactive waste at various point in the process in order to forman overall waste quantity to meet certain governmental or environmentalstandards.

“Radioactive cemented waste” means a radioactive waste, which has atsome time been in contact with a cement to thereby become “cemented”.

“Rare Earth Elements” (REE) means a compound containing at least oneelement of the rare earth elements (Scandium, Yttrium, Lanthanum,Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium,Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium,Lutetium) and may include solubilized ions, complexes, derivatives,isomers, as the case may be. For instance, the term “Rare Earth” mayinclude one of the light rare earth LREE (La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃)and/or one of the heavy rare earth HREE (Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₄O₇,Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃, Y₂O₃) in association withother elements or solubilized in an aqueous medium. Thus, these elementsshould be read with a mind to their relationship with the process steps,process conditions and other interacting compounds.

“Uranium” (U), “cesium” (Cs), “mercury” (Hg), “thorium” (Th), unlessspecified otherwise, each means a compound containing the given elementand may include solubilized ions, complexes, derivatives, isomers, asthe case may be. For instance, the term “uranium” may include uranium(IV) and uranium (VI); “cesium” may include cesium in association withother elements or solubilized in an aqueous medium; while “mercury” mayinclude the element in association with sulfur or oxygen, solubilized,or in its pure metallic form upon dissolution. Thus, these elementsshould be read with a mind to their relationship with the process steps,process conditions and other interacting compounds.

DETAILED DESCRIPTION OF SELECTED EXEMPLARY EMBODIMENTS

Embodiments of the present disclosure include an apparatus for grindingor comminuting, as well as optionally leaching, of ores, mine wastes andradioactive wastes. Therefore, selected embodiments provide an attritionmill for grinding and attrition of ores. In certain such embodiments theapparatus may be so effective or efficient that such ores and relatedsubstrates may undergo useful grinding without necessarily requiring thepresence, the expense or inefficiency of using grinding media. In turnthis makes the apparatuses defined herein especially useful for grindingan comminuting of radioactive ores and wastes, and the resulting outputor product from the apparatus is not complicated by a presence of thegrinding media that may have been made radioactive by the grindingprocess (and thus difficult to separate and dispose of). This in turnmakes the apparatuses, and corresponding methods that employ theapparatuses, more efficient and effective, since down-times for liningreplacements are reduced, larger quantities of ore may be ground(without the bulk of the grinding media) and there is no need orrequirement to separate the grinding media from the ground ore orradioactive waste after grinding is completed, as is the case for batchprocesses and most laboratory experiments. Further embodiments includethe use of such apparatuses, and corresponding methods that employ theapparatuses.

In the following detailed description section, specific embodiments aredescribed. However, to the extent that the following description isspecific to a particular embodiments or particular uses they areintended for exemplary purposes only and simply provide a description ofexemplary embodiments. Accordingly, the specification is not limited tothe specific embodiments described below, but rather, includes allalternatives, modifications, and equivalents falling within the scope ofthe present specification.

At the outset, for ease of reference, certain terms used in the presentspecification and their meanings as used in this context are set forth.To the extent a term used herein is not defined below, it should begiven the broadest definition persons in the pertinent art have giventhat term as reflected in at least one printed publication or issuedpatent. Further, the present specification is not limited by the usageof the terms shown below, as all equivalents, synonyms, newdevelopments, and terms or techniques that serve the same or a similarpurpose are considered to be within the scope of the presentspecification.

In one embodiment, a process for combined grinding and leaching of atleast one metal from ores or wastes, including radioactive wastes andmine wastes in one step has been developed. The process may comprise acombined attrition and leaching step, and a separation step. Thecombined attrition step and leaching step may comprise grinding andmixing of ore or waste with an aqueous inorganic acid to solubilize atleast one metal present in the ore or waste. Preferred metals forrecovery or separation may include uranium, cesium, mercury, thorium andrare earth elements, or any combination thereof.

The aqueous inorganic acid may preferably be in a concentration fromabout 1 M to about 9 M. The inorganic acid may be sulfuric acid, nitricacid, hydrochloric acid, phosphoric acid, or any mixtures thereof, ormay also be a combination of inorganic acid and corresponding salts. Theinorganic acid may be used acid or recycled acid. Preferably, theinorganic acid is sulfuric or nitric acid.

The combined attrition and leaching step with the aqueous inorganic acidmay be performed with a leaching salt. For example, the leaching saltmay be a halogen salt, such as iodine, chlorine, fluorine or bromine, orany combination thereof. The leaching salt may be a mercury salt, suchas mercury nitrate, mercury chloride, mercury iodide, mercury iodate, orany combination thereof. Preferably, the leaching salt is potassiumiodide or mercury nitrate, or any combination thereof. The salt may bein a concentration between about 0.01 M and about 1 M.

The combined attrition and leaching step may preferably be carried outat a temperature lower than about 100° C. to solubilize at least aportion of the at least one metal present in the ore or waste. Mixingmay be carried out for a period sufficient to solubilize the metals, forexample from about 0.1 h to about 24 h, preferably from 0.1 h to 2 h. Ametal-rich leachate and a metal-poor ore or waste may be formed from thecombined grinding and leaching step. The metal-rich leachate and themetal poor ore or waste may be separated for further processing torecover the metal. The separation step may be performed by any knownmethods such as ion exchange, solvent extraction, precipitation,membrane separation, or the like techniques known in the art ofcombinations thereof.

Optionally, the ore or waste may be crushed or screened according to anyknown methods to reduce the particle size of the ore or waste. Forexample, it may be reduced to a particle size inferior to about 15 cm,or preferably to a particle size inferior to about 15 mm.

Optionally, the amount of water and/or the amount of ore or waste thatare mixed together during the combined attrition and leaching step maybe adjusted to obtain an aqueous mixture having an ore or wasteconcentration between about 50 g/L and about 500 g/L of the totalmixture.

The process for combined grinding and leaching may optionally beperformed without the use of grinding media. Grinding in the absence ofgrinding media represents considerable advantages since it requires lessenergy and entrains important cost saving and reduction of GHGemissions. Grinding media are hard to separate from the pulp aftergrinding, especially in batch processes, and can neither be disposedwith the residual waste. The impact on mine operations and carbonfootprint reduction is also important considering the space occupied bythe grinding media in the grinding chamber and wear on the equipment.

According to another embodiment of the process, the combined attritionand leaching step may be repeated to include multiple sequential steps.The multiple combined attrition and leaching steps may use the same ordifferent conditions, for example the same or different inorganic acid,the same or different concentration of inorganic acid, the use of aleaching salt being the same or different, etc.

Furthermore, the process may comprise a washing step of the separatedmetal-poor ore or waste to remove residual metals. The washing step maycomprise any known method for removing residual metals. Optionally, thewashing step may comprise filtering the separated metal-poor ore orwaste to provide solids, rinsing or mixing the solids with a washingsolution and performing a solid-liquid separation to provide washedsolids and spent washing waters. The washing solution may comprisewater, a diluted acid solution, an acid solution, or the like.

The washing step may be performed multiple times, if required. The spentwashing waters may be used in a subsequent process for combined grindingor leaching or any other process for the treatment of ore and waste.

Other embodiments also provide a process for combined grinding andleaching comprising a basic combined attrition and leaching step, anacidic combined attrition and leaching step, and a separation step.

The basic combined attrition and leaching step may comprise grinding andmixing the ore or waste with an inorganic base. The inorganic base maybe in a solid form and used with water, or it may be in the form of anaqueous solution preferably in a concentration from about 1 M to about7.5 M. The inorganic base may include sodium hydroxide, potassiumhydroxide, calcium hydroxide, sodium carbonate, ammonia, or acombination thereof. The inorganic base may be used base or recycledbase. Preferably, the inorganic base is sodium hydroxide. The basiccombined attrition and leaching step may be carried out for about 0.01hour to about 1 hour.

The acidic combined attrition and leaching step may be the same aspreviously described, and may be performed multiple times, using thesame or different conditions. The separation step may also be as definedabove.

Example summaries of selected methods are illustrated in the flow chartsshown in FIGS. 1 and 2. FIG. 1 illustrates one method comprising a firststep of combined attrition and leaching, and a second step of separationof the leachate and the ore. FIG. 2 illustrates another methodcomprising a first step of basic combined attrition and leaching, asecond step of acidic combined attrition and leaching, and a third stepof separation of the leachate and the ore.

The processes for combined grinding and leaching defined above may beoperated in a modified attrition mill, or any known apparatus in theart.

Selected embodiments further provide for an apparatus for conducting aprocess for grinding, or optionally combined grinding and leaching, ofore or waste materials. Any of the methods and processes describedherein, in part or in full, may be conducted within, or with theassistance of, an apparatus as described herein.

Preferably, the apparatus is an attrition mill as described herein. Theattrition mill may comprise a grinding container or chamber, deviationbars, also termed elongate ribs, on or protruding from the wall and/orthe walls of the grinding container or chamber, a rotatably mountedshaft provided with a plurality of laterally extendinggrinding/attrition arms. The number of grinding/attrition arms, theirshape, length and relative configuration may be selected foroptimization of grinding efficiency and minimization of mill vibration.The shaft may be inserted into the grinding chamber and operativelyconnected to a motor for providing grinding and mixing of the mixturewithin the grinding chamber.

The deviation bars may be used to generate additional disturbances andshearing forces in the grinding process and in some embodiments mayassist in the grinding of the waste even in the absence of grindingmedia.

In some embodiments, the grinding container or chamber may be disposableor replaceable. In yet another embodiment, the apparatus may comprise anintegrated air flotation system as herein described. The air flotationsystem may assist separation of the metal from the ore or waste.

An exemplary apparatus is provided in FIGS. 3 to 7, where an attritionmill comprises a disposable container or grinding chamber 2 equippedwith deviation bars or elongate “ribs” 4 installed on and projectingfrom the inner wall and/or the floor surfaces of the container 2. In theembodiment illustrated the specifications of the exemplary modifiedattrition mill apparatus of the designed disposal grinding chamber wereas follow: 1) external diameter: 610 mm; 2) wall thickness: 8 mm; 3)shaft 6 diameter: 65 mm and 4) deviation bars (also known as elongateribs) 4: size 300×19×6 mm (L×D×T). The resulting clearance between shaft6 and its attached deviation bars, and grinding chamber 2, is 3 mm atthe bottom and 11.5 mm on the side.

Two dominant breakage mechanisms take place in this equipment: breakageby impact and breakage by attrition. The larger blocks or chunks of orefirst break by impact either among themselves and/or against thedeviation bars as they are moved by the grinding/attrition arms withinthe grinding chamber. As the blocks get smaller they are trapped at thebottom of the grinding chamber between the “lower-most”grinding/attrition arm(s) and the deviation bars or ribs 4 extending ona floor surface of the container 2, where they become further reduced insize by attrition. The clearance between the “lower-most”grinding/attrition arm(s) and the deviations bars in part controls thesize distribution of the end product. A clearance that is too small(e.g. smaller than 3 mm) is not recommended for some ores or wastematerials, at least in some embodiments, as it may increase the risk ofbars bending and blockage of the mixer. However, disclosed embodimentsare not limited in this regard. The size of the deviations bars can alsobe varied. They are designed for introducing minimum degrees ofturbulence that is required for breaking the larger blocks byimpact/grinding. In selected embodiments, the design of the deviationbars or ribs avoids larger perturbation of the flow, which can bedetrimental to the operation of the grinding mill.

One potential identified problem is the trapping of the blocks betweenthe grinding/attrition arms.

A number of experiments have shown that, under standard materialconditions, the dimensions of the shaft and the number ofgrinding/attrition arms may have limited impact on the product sizedistribution and the efficiency of the grinding mill. The spacing amongthe bars however is preferably sufficiently large for avoiding trappingof the larger blocks within the shaft arm, which reduces their grindingefficiency and even stops their size reduction. Based on thisobservation the number of mixer arms may, at least in some but not allexemplary embodiments, be limited to 8 bars spaced at 4 inches and by anangle of about 40′. The spacing between the “lower-most”grinding/attrition arm(s) may optionally be reduced to 2 inches at thebottom of the grinding chamber where finer blocks accumulate beforebeing further reduced in size by attrition. The “lower-most”grinding/attrition arm(s) form is also of importance: a square orrectangular cross-sectional form is sometimes preferred for increasingthe shearing surface and the overall efficiency of the attritionbreakage mechanism (best illustrated, for example, in feature 10′ ofFIG. 7—see below—but also illustrated in other Figures).

It was demonstrated through a number of experiments that the minimalfloor and wall thickness of the disposable grinding chamber 2 can, insome selected embodiments, be further reduced to 3 mm. These experimentswere done with radioactive waste; a more resistant rock material mayeventually require a more resistant and therefore larger wall thickness.

A telescopic head may optionally be provided for moving the attritionunit shown generally at 8 (shaft 6 and attrition arms 10) up and down asrequired, and to allow the displacement (or e.g. replacement) of thecontainer or chamber, or for servicing of the attrition unit. Operatingconditions were developed accordingly for lowering progressively theshaft 6 of the attrition unit 8 in a bed of ore or waste blocks.Rotation speed of the mixer was also increased progressively as neededto avoid unacceptable vibration of the apparatus. In both cases theincreased rate was a function of material size and hardness and wastherefore experimentally defined for each application. All equipmentpieces were made of stainless steel 316 for meeting the lixiviationprocess requirements. The above specifications were selected forminimization of mill vibration and optimization of the size reductionratio. It was demonstrated that, at least in some embodiments, themodified attrition mill was able to grind ore and waste blocks from a80% passing size of about 15 cm down to 4 mm. However, it will beunderstood that such embodiments are merely exemplary, and others may beincluded with any modifications necessary within the scope of thepresent disclosure.

In further exemplary embodiments, a magnetic separator (see FIG. 6),made for example of neodymium magnets 14, may be attached to the shaftarm assembly of the mixer, which was designed at the laboratory scaleand successfully tested at the pilot scale. The magnets were attached tothe mixer shaft assembly for increasing the probability of collision ofthe grinding/attrition arms with metal pieces, fragments or particles inthe ore or waste material in the hope of increasing their recovery. Ametal recovery of 88% clean at 70% was obtained at the pilot scale. Thecleanliness of the metal recovered with the laboratory version of theseparator was slightly better at 78%. Two types of magnet arrangementswere tested (FIGS. 6 and 7): one consisting of axially magnetizedcylinder or bar 14 (FIG. 6) while the other was made of bars magnetizedthrough their thickness (FIG. 7). Both magnet arrangements are shown inFIG. 7. Despite a reduced collection zone, axially magnetized cylinderswere found to be somewhat more efficient than metal bars magnetizedthrough their thickness during these initial tests. The magnetic fieldis maximal at both extremities with the axially magnetized cylinder andthis design appears to be well suited for collecting residual iron 15,which appears to concentrate at the bottom of the grinding chamber. Sucha behavior of the iron is quite comprehensive considering the lowagitation speed in the grinding chamber and the high density of iron.The design of an electromagnet equivalent is simplified and theelectromagnet may alternatively be integrated into the shaft armassembly. Other configurations for integrations of magnets or magneticsystems are also contemplated.

FIG. 7 illustrates a further optional feature that may present certainadvantages depending upon the ore or material subjected to grinding inthe attrition mill. As illustrated, most of the attrition arms 10 (alsoherein termed grinding arms) extending from the shaft have a circular orelliptical cross-section. However, as can be seen in the illustrationshown in FIG. 7 the “lower-most” pair of arms 10′ extending from theshaft nearest the closed end of the container (i.e. nearest the floor ofthe container) may have a substantially square or rectangular ratherthan circular or elliptical cross-section. As illustrated, suchattrition arms 10′ (or grinding arms) have a generally squarecross-section with rounded corners (in cross-section). This profile ofthe lower-most attrition arms adjacent the ribs projecting or protrudingon the inside floor of the container or chamber, may help to improve arate of attrition of the ore or waste, thereby to improve grindingefficiency.

Optionally, an air flotation system may be integrated into the modifiedattrition mill in order to help separate finely broken pieces of e.g.plastic or to perform flotation of selected minerals (see FIG. 5). Inone example modifications as shown for example in FIG. 5 may be asfollows: 1) 12 mm diameter hole was drilled within the shaft 6 and thesecond mixer bottom attrition arm 10A; 2) 10 air diffusers (460 μm) wereinstalled on the mixer second bottom attrition arm 10A as air nozzles12; 3) air flow was introduced within a seal at the top of the shaft 6and; 4) a manual valve was installed on the air line for controlling theflow (not shown). An air flotation system may also be used as an airaddition unit for the lixiviation process. Air diffusers may also beinstalled in other portions of the attrition mill as required.

FIGS. 8 to 16 illustrate yet further embodiments of the attrition millapparatus. For example, FIG. 8 illustrates an apparatus in which theattrition mixer unit 16 (comparable to 8 shown in FIG. 5) is removedaxially from the container 17 (comparable to 2 in FIGS. 3 and 4). InFIG. 9 the elongate deviation bars or ribs 18 on the inside surface ofthe container (corresponding to 4 in FIG. 3) are visible on the innerwalls of the container. In FIG. 10 the grinding arms 19 (also termedattrition bars) extending from the main shaft 20 of the attrition unitare visible in the container as the attrition unit is positionedco-axially into the container. As shown, the grinding bars are shown inan optionally, generally helical arrangement about the shaft.

FIGS. 11 to 16 illustrate a similar apparatus, but with FIGS. 14 to 16illustrating a smaller-scale apparatus compared to FIGS. 11 to 13.Nonetheless the features of the apparatus correspond substantially tothose shown in FIGS. 8 to 10, with some exceptions. In FIG. 13 only fourdeviation bars or ribs 18 are shown on the inner walls of the container(in two opposing pairs). Furthermore, in FIGS. 11 and 12 the grindingarms (attrition arms) 17 of the attrition unit are shown in alternating90 degree offset arrangement between adjacent grinding arms along theshaft. Such arrangement may be preferred in some circumstances dependingupon the ore or waste to be processed.

Embodiments of the present invention provide a number of advantages.Advantages will be understood as per the above and the examples andexperimental data obtained through the extensive studies presentedbelow. In some but not all embodiments, the apparatuses herein disclosedmay be suitable for a combining grinding and leaching of ore or waste ina single step in the apparatus, which may improve leaching and grindingefficiencies, may reduce process steps and energy consumption, maysimplify equipment, and may reduce both of the CAPEX/OPEX.

EXAMPLES

While the present specification may be susceptible to variousmodifications and alternative forms, the embodiments will now bedescribed by way of examples. However, it should again be understoodthat the specification is not intended to be limited to the particularexamples disclosed herein. Indeed, the present specification includesall alternatives, modifications, and equivalents falling within thescope of the present specification.

General Methodology

The following describes the general methodology of examples ofembodiments of the process and apparatus of the present invention.

Radioactive Wastes

The experiments described below were carried out with radioactivecemented wastes prepared at CanmetMINING. The procedure involves mixinga synthetic solution with either General Use (GU) or High Early Strength(HE) cements manufactured by Lafarge Canada Inc., in a manner thatmimics the process carried out at CNL. The solid wastes batches wereallowed to age and were subsequently removed from the pails with an airhammer. The whole pail content (^(˜)20 kg) was crushed in a laboratoryjaw crusher (Retsch, model BB200) to the selected particle size and thensplit into representatives fractions using a large capacity (20 kg)rotary splitter (GENEQ, model SEO4OJ-001). Table 1 shows theexperimental conditions used to prepare two radioactive wastes and theirpartial compositions.

TABLE 1 Main experimental parameters used to prepare solid wastesbatches and partial composition Solution to Batch Cement Cement AgingAging Cs Hg U Code Type Ratio Time Temperature ppm ppm ppm U28 GU 0.3930 months 60° C. 8.5 1,973 1,150 U29 GU 0.29 30 months Ambient 7.2 1,9771,104

Ores

Experiments were conducted using six ores of rare earth elements (1carbonatite, 4 peralkalines, 1 sedimentary). The ores were provided bysix different mining companies and used as received. Table 2 shows thechemical compositions.

TABLE 2 Chemical composition of the six ores of rare earth elementsPeralkaline Peralkaline Peralkaline Peralkaline Carbonatite SedimentaryOre A ore B ore C ore D ore ore ore Th (ppm) 53 313.4 936.9 379.3 155.3285.8 U (ppm) 17.6 31.6 151.3 22.7 18 264.2 Y (ppm) 1507 949.5 3854 121355 50.1 La (ppm) 2517 433.7 1579 2032 3662 340.4 Ce (ppm) 5752 1086 35264031 7427 623.4 Pr (ppm) 672 136.1 368.1 448.1 769.4 63.9 Nd (ppm) 2603531.4 1239 1586 2574 207 Sm (ppm) 554.1 117.1 319.5 276.1 244 37.4 Eu(ppm) 67.5 14.6 20.7 14 43.2 2.3 Gd (ppm) 535.8 117.4 358.3 239.6 115 26Tb (ppm) 83.2 21.5 81.3 34.8 7.3 2.9 Dy (ppm) 454.3 146.9 609.4 208 19.212.5 Ho (ppm) 75 32.6 139.4 39.7 2.4 1.9 Er (ppm) 177 106.4 452.4 1126.9 4.5 Tm (ppm) 19.3 16.1 67.1 15.3 0.4 0.6 Yb (ppm) 101.6 109.5 413.492.9 2.8 3.9 Lu (ppm) 10.5 14.1 51.1 11.2 0.5 0.5

Grinding and Leaching Experiments

Three attrition cells (1.2 L, 12 L and 120 L) were designed to conductgrinding and leaching experiments on the different cemented wastes andthe six different ores of rare earth elements. Testing were performedusing wastes and ores at different pulp density and using differentparticle size materials. Inorganic base and leaching salt were added tothe ore or waste at the beginning of the attrition tests. The inorganicacid was added using a peristaltic pump during the experiments at afixed flow rate. Temperature and pH were recorded during theexperiments.

Analytical

Liquid samples were analyzed by ICP-MS (Thermo-Fisher Scientific,X-Series II), after appropriate dilution with HCl to stabilize theHg(II). Solid samples acid digestion was done by microwave, analyzed byICP-MS and compared with certified reference materials of REE ores.

Example 1: Grinding and Leaching of Radioactive Wastes in a ModifiedAttrition Mill

Various radioactive cemented wastes were cured at 60° C. and/or agedduring 30 months were subjected to grinding and leaching in the modifiedattrition mill. These radioactive cemented wastes were U28 (30 months at60° C.), U29 (30 months at ambient temperature). Initial concentrationof Cs, Hg, and U are given in Table 1. FIG. 17 is a diagram showing thesolubilization of the U29 radioactive cemented waste in the modifiedattrition mill by combining grinding and leaching with sulfuric acid atdifferent particle size and with or without rinsing (pulp density fixedat 20%, acid/cement ratio fixed at 1.75). The U29 radioactive cementedwaste was crushed at different particle size (6 mm, 8 mm, 12 mm).Samples of 100 g were mixed with 500 mL of distilled water to obtainpulp density of 20%. Then pure sulfuric acid was added using aperistaltic pump (6 mL/min flowrate) to obtain a fixed acid/cement ratioof 0.75 (about 1.5 M). The acid/cement ratio is a key parameter ascement dissolution and U solubilization are pH dependent. The acidconsumption depends on the particle size of the cement after grinding.The pH needs to be comprised between 1.5 and 2 to enhance Usolubilization. Samples were subjected to combine grinding and leachingin the small attrition cell (1.2 L) as show in FIGS. 14 to 16 during 1h. The processing of radioactive wastes at different particle size inthe modified attrition mill allows an efficient solubilization of Cs andU with solubilization yields of 90-100% and 88-98% respectively. Theaddition of a rinsing step (8 mm R) increases significantly thesolubilization yields of Cs, Hg, and U. The Hg solubilization yields arebetween 50% and 60%, but Hg solubilization will be enhanced using aleaching salt. This is due to the mineralogy of the cemented waste.Uranium phases are found mainly as long layers (400 μm) and some smallgrains. Mercury phases are found as grains below 20 μm and the smallgrains that tend to agglomerate with longer aging times and higher agingtemperatures. Moreover, the proportion of metallic mercury and mercurysulfide appears to increase with aging times and aging temperatures.

Example 2: Influence of Pulp Density and Addition of a Leaching Salt

The U29 radioactive cemented waste crushed at 12 mm was used toinvestigate the influence of pulp density and the addition of theleaching salt. Samples of 100 g and 200 g were mixed with 500 mL ofdistilled water to obtain pulp density of 20% and 40% respectively.Potassium iodide was added as leaching salt to obtain a concentration of0.06M to enhance Hg solubilization. Then pure sulfuric acid was addedusing a peristaltic pump (6 mL/min flowrate) to obtain a fixedacid/cement ratio of 0.75 (about 1.5 M for 20% pulp density and 3M for40% pulp density). The acid consumption depends on the particle size ofthe cement after grinding. The pH needs to be comprised between 1.5 and2 to enhance U solubilization. Samples were subjected to combinegrinding and leaching in the small attrition cell (1.2 L) as shown inFIGS. 14 to 16. FIG. 18 is a diagram showing the solubilization of theU29 radioactive cemented waste in the modified attrition mill bycombining grinding and leaching with sulfuric acid at different pulpdensity and with or without salt (particle size fixed at 12 mm,acid/cement ratio fixed at 1.75). The processing of radioactive wastesat different pulp density in the modified attrition mill allows anefficient solubilization of Cs and U with solubilization yields above95% for Cs and 85% for U for pulp density of 20% or 40%, respectively.The leaching salt increase the Hg solubilization from 65% to 79% at 20%pulp density and from 52% to 63% at 40% pulp density.

Sulfuric acid and potassium iodide improve the solubilization of Hg byoxidation of all the mercury species and form mercury tetraiodidecomplex (HgI₄ ²⁻, Kf=2.10³⁰). Sodium chloride formed mercury complex(HgCl₄ ²⁻, Kf=5.10¹⁵) when Hg is present as mercury oxide HgO ormetallic mercury Hg⁰ in 30 months aged wastes but not with mercurysulfide HgS (pK=52) formed in 60° C. cured wastes. In order to oxidizeHg⁰, as well as HgS, tests were performed using iodide halogen salt asstrong oxidant to form Hg complex (HgI₄ ²⁻, Kf=2.10³⁰).

Example 3: Grinding and Leaching of Radioactive Wastes in a LargeModified Attrition Mill

The U28 radioactive cemented waste (aged 30 months at 60° C.) crushed at8 mm was used to investigate the influence of the addition of theleaching salt. Samples of 800 g were mixed with 3674 mL of distilledwater to obtain pulp density of 20%. Potassium iodide (masses of 40, 80,120, and 160 g) was added as leaching salt to obtain a concentration of10 to 40 g/L to enhance Hg solubilization. Then pure sulfuric acid wasadded using a peristaltic pump (33 mL/min flowrate) to obtain a fixedacid/cement ratio of 0.75 (about 1.5 M for 20% pulp density). Sampleswere subjected to combine grinding and leaching in the large attritioncell (12 L) as show in FIGS. 11 to 13.

FIG. 19 is a graph to show solubilization of U28 radioactive cementedwaste in an apparatus by combining grinding and leaching with sulfuricacid at different salt concentration (particle size fixed at 8 mm,acid/cement ratio fixed at 1.5). The processing of radioactive wastes atdifferent acid concentration in the large modified attrition mill allowsan efficient solubilization with solubilization yields above 99% for Csand U at potassium iodide concentration of 20 and 30 g/L, respectively.Best Hg solubilization was obtained at potassium iodide concentration of30 g/L. Sulfuric acid and potassium iodide improve the solubilizationfrom wastes aged 30 months at 60° C.

Example 4: Grinding and Leaching of REE Ores in a Modified AttritionMill Using Sulfuric Acid

Experiments on ores were conducted using six ores of rare earth (1carbonatite, 4 peralkalines, 1 sedimentary). The coarse ores (2-3 mm)were provided by six different mining companies and used as received.Theses ores were subjected to grinding and leaching in the modifiedattrition mill. A 100 g sample of ore was mixed with 250 mL of distilledwater to obtain a 40% pulp density. Then pure sulfuric was added using aperistaltic pump (6 mL/min flowrate) to obtain a fixed acidconcentration of about 7.5 M and a final pulp density of about 20%.Samples were subjected to combined grinding and leaching in the smallattrition cell (1.2 L) as show in FIGS. 14 to 16 during 1 h. Initialconcentration of Th, U and rare earth elements (REE) in each ores aregiven in Table 2. NaOH additions were performed to enhance metalssolubilization. For this purpose, the ore was grind with 25 g of NaOHpellets during 15 minutes at 40% pulp density before the addition ofacid. FIG. 20 is a diagram showing the solubilization of Th, U, and REEfrom the 6 ores in the modified attrition mill by combining grinding andleaching with sulfuric acid with or without NaOH addition performed atroom temperature during 1 h (pulp density fixed at 20%, acidconcentration fixed at 7.5M).

For the C ore, solubilization yields with and without NaOH reached24-55% for Th, 32-43% for U, 3-17% for light rare earth and 9-23% forheavy rare earth. For the Sed. ore, solubilization yields with andwithout NaOH reached 46-87% for Th, 80-93% for U, 7-31% for light rareearth and 33-57% for heavy rare earth. For the D ore, solubilizationyields with and without NaOH reached 7-74% for Th, 13-26% for U, 2-16%for light rare earth and 5-24% for heavy rare earth. For the Carb. ore,solubilization yields with and without NaOH reached 0-2% for Th, 9-20%for U, 0-1% for light rare earth and 0-3% for heavy rare earth. For theB ore, solubilization yields with and without NaOH reached 2-39% for Th,27-41% for U, 2-36% for light rare earth and 6-33% for heavy rare earth.For the A ore, solubilization yields with and without NaOH reached 1-27%for Th, 10-16% for U, 0-14% for light rare earth and 2-12% for heavyrare earth.

The grinding and leaching in the modified attrition mill using sulfuricacid is efficient for most of the ores but the addition of NaOH do notincrease the solubilization of Th, U, and REE.

Example 5: Grinding and Leaching of REE Ores in a Modified AttritionMill Using Nitric Acid

Experiments on ores were conducted using six ores of rare earth (1carbonatite, 4 peralkalines, 1 sedimentary). Theses ores were subjectedto grinding and leaching in the modified attrition mill. A 100 g sampleof ore was mixed with 250 mL of distilled water to obtain a 40% pulpdensity. Then pure nitric acid was added using a peristaltic pump (6mL/min flowrate) to obtain a fixed acid concentration of about 7.5 M anda final pulp density of about 20%. Samples were subjected to combinegrinding and leaching in the small attrition cell (1.2 L) as show inFIGS. 14 to 16 during 1 h. Initial concentration of Th, U and rare earthelements (REE) in each ores are given in Table 2. NaOH additions wereperformed to enhance metals solubilization. For this purpose, the orewas ground with 25 g of NaOH pellets during 15 minutes at 40% pulpdensity before the addition of acid. FIG. 21 is a diagram showing thesolubilization of Th, U, and REE from the 6 ores in the modifiedattrition mill by combining grinding and leaching with nitric acid withor without NaOH addition performed at room temperature during 1 h (pulpdensity fixed at 20%, acid concentration fixed at 7.5M).

For the C ore, solubilization yields with and without NaOH reached61-66% for Th, 27-30% for U, 15-16% for light rare earth and 19-20% forheavy rare earth. For the Sed. ore, solubilization yields with andwithout NaOH reached 89-99% for Th, 98-99% for U, 22-83% for light rareearth and 48-99% for heavy rare earth. For the D ore, solubilizationyields with and without NaOH reached 55-77% for Th, 8-9% for U, 7-10%for light rare earth and 10-13% for heavy rare earth. For the Carb. ore,solubilization yields with and without NaOH reached 91-99% for Th,29-32% for U, 85-91% for light rare earth and 84-94% for heavy rareearth. For the B ore, solubilization yields with and without NaOHreached 56-80% for Th, 43-54% for U, 61-77% for light rare earth and54-65% for heavy rare earth. For the A ore, solubilization yields withand without NaOH reached 25-30% for Th, 8-9% for U, 22-23% for lightrare earth and 11-12% for heavy rare earth.

The grinding and leaching in the modified attrition mill using nitricacid is very efficient and the addition of NaOH increases significantlythe solubilization of Th, U, and REE for most of the ores. The grindingand leaching of ores in the modified attrition mill using nitric acid isthe most efficient.

Example 6: Grinding and Leaching of REE Ores with a Leaching Salt

Experiments of grinding and leaching of ore in the modified attritionmill using a leaching salt were done using the C ore of rare earth. A100 g sample of ore was mixed with 250 mL of distilled water to obtain a40% pulp density. Then pure sulfuric or nitric acid was added using aperistaltic pump (6 mL/min flowrate) to obtain a fixed acidconcentration of about 7.5 M and a final pulp density of about 20%.Samples were subjected to combine grinding and leaching in the smallattrition cell (1.2 L) as show in FIGS. 14 to 16 during 1 h. Initialconcentration of Th, U and rare earth elements (REE) in the C ore isgiven in Table 2. NaOH additions were performed to enhance metalssolubilization. For this purpose, the ore was ground with 25 g of NaOHpellets during 15 minutes at 40% pulp density before the addition ofacid. Leaching salts were added to enhance metals dissolution (Reynieret al., 2015; Mellor, 1930; Kitts et Perona, 1957).

FIGS. 22 and 23 are diagrams showing the solubilization of Th, U, andREE from the C ore in the modified attrition mill by combining grindingand leaching with a) sulfuric acid in FIG. 22 and b) nitric acid in FIG.23 with or without NaOH addition and salt addition (KI or Hg(NO₃)₂)performed at room temperature during 1 h (pulp density fixed at 20%,acid concentration fixed at 7.5 M, salt concentration fixed at 0.06 Mfor KI and 0.03 M for Hg(NO₃)₂). In FIG. 22, the combined grinding andleaching of the C ore in sulfuric acid is improved significantly by theaddition of potassium iodide as a leaching salt. Solubilization yieldswith KI reached 86.6±5.3% for Th, 58.1±9.4% for U, 15.4±3.9% for lightrare earth and 28.3±4.9% for heavy rare earth.

In FIG. 23, the combined grinding and leaching of the C ore in nitricacid is improved significantly by the addition of mercury nitrate as aleaching salt. Solubilization yields with Hg(NO₃)₂ reached 98.0±3.2% forTh, 68.7±11.0% for U, 27.0±5.9% for light rare earth and 41.1±5.6% forheavy rare earth.

The grinding and leaching of ores in the modified attrition mill usingnitric acid is the most efficient. The addition of a leaching salt(potassium iodide or mercury nitrate or a combination thereof) increasessignificantly the solubilization of Th, U, and REE from the C ore.

Example 7: Grinding and Leaching of REE Ores in a Large ModifiedAttrition Mill

Experiments on ores were conducted using six ores of rare earth (1carbonatite, 4 peralkalines, 1 sedimentary). The coarse ores (2-3 mm)were provided by six different mining companies and used as received.Theses ores were subjected to grinding and leaching in the largemodified attrition mill. A 500, 1000 or 1500 g sample of ore was mixedwith 3350 mL of distilled water. Then pure acid was added using aperistaltic pump (50 mL/min flowrate) to obtain a fixed acidconcentration of about 30% and a final pulp density of about 10, 20, or30%. Samples were subjected to combined grinding and leaching in thelarge attrition cell (12 L) as shown in FIGS. 11 to 13 during 2 h. FIG.24 is graph to show solubilization of Th, U, and REE from 3 of the oresin a modified attrition mill by combining grinding and leaching withnitric acid performed at 75° C. for 2 h at different pulp density and anacid concentration fixed at 30%). Solubilization of Th, U, LREE, andHREE remains stable when processing the REE ores in the large modifiedapparatus at different pulp density. The pulp density may be increasedto grind and leach more materials at the same time. Results obtained forSed. ore, Carb. ore, and Peralkaline B ore are very promising. Thesolubilization efficiencies were not affected when using a largemodified grinding apparatus at different pulp density.

FIG. 25 is graph to show solubilization of Th, U, and REE from 3 of theores in a modified attrition mill by combining grinding and leachingwith different acid (sulfuric, nitric, hydrochloric) performed at 75° C.for 2 h with acid concentration fixed at 30%. These experiments wereperformed at 20% pulp density (by using 1000 g of REE ore). For theperalkaline ores A, C, and D, solubilization yields are lower than forthe 3 others ores due to their respective mineralogy but the processusing the large modified apparatus was still efficient. The combinedgrinding and leaching using sulfuric acid achieved better results thanhydrochloric and nitric acids for these ores.

The addition of a leaching salt (potassium iodide or mercury nitrate ormercury tetraiodide) is expected to increase solubilization of Th, U,and REE from these ores.

REFERENCES

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1. An apparatus for grinding or comminuting a metal-containing ore,substrate, mine waste, or radioactive waste, the apparatus comprising:a. a container comprising inner walls that define an open end and aclosed end for the container, and a lumen for retaining the ore, withtwo or more elongate ribs projecting inwardly from the walls andextending from the closed end towards the open end of the container; b.a powered, rotatable spindle extending into and axially aligned with thecontainer, substantially equidistant from side walls of the inner wallsof the container; c. a plurality of grinding arms arranged about andextending from the spindle such that each comprises at least one freeend that passes with a clearance of from 0.01 mm to 20 mm from each ofthe ribs on the inner walls of the container, as the spindle is rotated;and d. a motor to drive axial rotation of the spindle and attachedgrinding arms within the container, wherein the apparatus grinds orcomminutes the metal-containing ore, substrate or mine waste by grindingand attrition, optionally absent grinding media.
 2. The apparatus ofclaim 1, wherein each grinding arm extends through and extends upon eachside of the spindle such that each grinding arm comprises two free endsthat each pass with a clearance of from 0.01 mm to 20 mm from each ofthe ribs on the side walls of the container, as the spindle is rotated.3. The apparatus of claim 1, wherein successive grinding arms arearranged helically about the spindle such that each successive grindingarm extends at an acute angle from the axis of the spindle relative toits adjacent grinding arm on the spindle, and all grinding arms extendabout 90 degrees from an axis of the spindle.
 4. The apparatus of claim1, wherein each grinding arm extends about 90 degrees from each adjacentgrinding arm along the spindle, and all grinding arms extend about 90degrees from an axis of the spindle.
 5. The apparatus of claim 1,wherein the grinding arms are at least substantially uniformlyelliptical in cross-section, or at least substantially uniformlycircular in cross-section, and optionally the grinding arm or armsadjacent the closed end of the container have a substantially square orrectangular cross-section.
 6. The apparatus of claim 1, wherein thespindle and attached grinding arms are movable axially relative to thecontainer such that the spindle and grinding arms can be removed fromthe container, optionally by a telescoping attachment arm.
 7. Theapparatus of claim 1, wherein the container comprises three or moreribs, at least a portion of which are arranged at least substantiallyparallel to one another in a radially symmetric manner about the innerwalls of the container.
 8. The apparatus of claim 7, wherein thecontainer defines a cylindrical lumen and the side inner walls comprisesix ribs arranged parallel to one another, at least a portion of whichextend a length of the side inner walls from the closed end to the openend of the container, in a radially symmetrical arrangement 60 degreesapart about the axis of the container.
 9. The apparatus of claim 1,wherein the inner walls of the container define a cylindrical lumen forthe container, defined by a continuous, cylindrical side wall portionextending between the open and closed ends of the container, and asubstantially circular floor portion at the closed end of the container,the elongate ribs extending such that they radiate from a centre of saidcircular portion and continue with a substantially parallel arrangementalong said cylindrical side wall portion from the closed end to the openend of the container.
 10. The apparatus of claim 1, wherein theplurality of grinding arms comprises from 2 to 20 grinding arms.
 11. Theapparatus of claim 1, wherein clearance between the free ends of thegrinding arms and the ribs is from 0.1-5 mm.
 12. The apparatus of claim9, wherein the grinding arms comprising one or more grinding arms thatextend from a free-end of the spindle, which during operation androtation of the spindle pass adjacent the portion of the elongate ribsthat radiate from a centre of the substantially circular floor portionat the closed end of the container, with a clearance of from 0.5-10 mm,preferably less than 5 mm, preferably less than 3 mm.
 13. The apparatusof claim 1, wherein the powered, rotatable splindle and/or the grindingarms comprise one or more magnets for collecting magnetic metalcomponents of the ore, substrate or mine waste.
 14. The apparatus ofclaim 1, further comprising air floatation means to add pressured airinto the ore, substrate or mine waste being processed, the airfloatation means comprising air channels extending within at least someof the grinding arms, each of which exits at least part way along itsrespective grinding arm, and an air pump to force air through the airchannels and out of the grinding arms during rotation of the spindle.15. A method for grinding or comminuting a metal-containing ore,substrate, mine-waste, or radioactive waste, comprising the steps of: a.adding the metal-containing ore, substrate or mine waste to thecontainer of the apparatus of claim 1; b. optionally adding a grindingmedia; and c. applying power to the motor thereby to rotate the spindleand attached grinding arms, to grind or comminute the metal-containingore, substrate, mine-waste, or radioactive waste; wherein step a., andoptional step b. if present, may be performed in any order.
 16. Themethod of claim 15, further comprising a step of adding to themetal-containing ore, substrate or mine waste, either before, togetherwith or after step a., an aqueous inorganic acid at a concentration ofbetween about 1M and about 9M, at a temperature of less than about 100°C., to solubilize at least a portion of the at least one metal, therebyto produce a mixture of a metal-rich leachate and a metal-poor ore orwaste.
 17. The method of claim 15, wherein the metal comprises uranium,cesium, mercury, thorium, rare earth elements, or combinations thereof.18. The method of claim 15, wherein the waste is a cemented radioactivewaste or a radioactive mine waste.
 19. The method of claim 16, whereinthe inorganic acid comprises sulfuric acid, nitric acid, hydrochloricacid, phosphoric acid, mixtures thereof, or combinations of inorganicacid and salts thereof.
 20. The method of claim 16, further comprising,either before or after the adding of the aqueous inorganic acid, a stepof adding an aqueous inorganic base with the addition of water, or withan aqueous organic base at a concentration of from about 1M to about7.5M, to solubilize at least a portion of the at least one metalproviding an aqueous mixture.
 21. The method of claim 15, furthercomprising addition of a leaching salt, wherein the leaching saltcomprises a halogen salt such as potassium iodide or a mercury salt suchas mercury nitrate, or any combination thereof.
 22. The method of claim16, further comprising a step of: separating the mixture of a metal-richleachate and a metal-poor ore or waste.
 23. The method of claim 15,wherein the method is performed absent any grinding media.